George M. Sheldrick

Bio: George M. Sheldrick is an academic researcher from University of Göttingen. The author has contributed to research in topics: Crystal structure & Bond length. The author has an hindex of 58, co-authored 791 publications receiving 151229 citations. Previous affiliations of George M. Sheldrick include University of Regensburg.

Reaktionen von Hexafluoraceton mit Alkalicyanaten

Abstract: NaSCN und KOCN reagieren mit Hexafluoraceton (HFA) im Molverhaltnis 1:2 unter Abbau des Anions in einem Schritt zu den Hexafluorpropanimin-Derivaten (CF3)2CNC(CF3)2OM (2a, b) (MNa, K), wahrscheinlich uber (CF3)2CN– als Zwischenstufe. Die Hydrolyse von 2a in Gegenwart wasriger Tetraphenylphosphoniumchlorid-Losung ergibt ein kristallines Hydrat der Zusammensetzung[(CF3)2C(OH)2·(CF3)2C(O)OH]– Ph4P+ (3). Im Kristall liegen dimere Dianionen vor, die uber vier asymmetrische und zwei symmetrische Wasserstoff-Bruckenbindungen verknupft sind. In einer unubersichtlichen Reaktion entsteht bei einem Reaktandenverhaltnis KSCN/HFA von 1:1 die polycylische Bisspiroverbindung 5. Kaliumselenocyanat reagiert mit HFA unter C – Se-Bindungsspaltung und nachfolgender Bildung des CF3-substituierten Oxazolidins 6. Die Rontgenstrukturanalysen von 2a, 3, 5 und 6 werden mitgeteilt. Reactions of Hexafluoroacetone with Alkali Cyanates NaSCN and KOCN react with hexafluoroacetone (HFA) in a molar ratio of 1:2 in a one-step reaction to yield the hexafluoropropanimine derivatives (CF3)2CNC(CF3)2OM (2a, b) (MNa, K). (CF3)2CN– is a possible intermediate. Hydrolysis of 2a in aqueous tetraphenylphosphonium chloride solution yields a crystalline hydrate of composition [(CF3)2C(OH)2·(CF3)2C(O)OH]– Ph4P+ (3). In the solid state dimeric dianions are observed, which are connected via four asymmetrical and two symmetrical O H O bonds. Starting with a 1:1 KSCN/HFA stoichiometry the polycyclic bisspiro compound 5 is formed in a complex reaction. In the reaction of potassium selenocyanate with HFA the C–Se bond is cleaved and the CF3-substituted oxazolidine 6 is formed. The X-ray structure analyses of 2a, 3, 5 and 6 are reported.

Crystal and molecular structure of the quinoxaline antibiotic analog TANDEM (des-N-tetramethyltriostin A)

Abstract: The crystal structure of TANDEM (des-N-tetramethyltriostin A), a synthetic analogue of the quinoxaline antibiotic triostin A, has been determined independently at -135 and 7 'C and refined to R values of 0.088 and 0.147, respectively. The molecule has approximate 2-fold symmetry, with the quinoxaline chromophores and the disulfide cross-bridge projecting from opposite sides of the peptide ring. The quinoxaline groups are nearly parallel to each other and separated by about 6.5 A. The peptide backbone resembles a distorted antiparallel 13 ribbon joined by intramolecular hydrogen bonds N-H(LVal)--O(L-Ala). At low temperatures, the TANDEM molecule is surrounded by a regular first- and second-order hydration sphere containing 14 independent water molecules. At room temperature, only the first-order hydration shell is maintained. Calculations of the interplanar separation of the quinoxaline groups as a function of their orientation with respect to the peptide ring support the viability of TANDEM to intercalate bifunctionally into DNA.

Synthesis of (diphenylphosphinothioyl)methyldiphenylphosphoniomethanide complexes of gold and silver. X-ray structure of [Au(C6F5){SPh2PCH-[Au(C6F5)]PPh2Me}]

Abstract: Both [Au(C6F5)3(SPh2PCHPPh2Me)]{obtained from [Au(C6F5)3(OEt2)] and [SPh2PCH2PPh2Me]ClO4, followed by deprotonation with NaH} and the free methanide SPPh2CHPPh2Me react with gold(I) or silver(I) complexes [Au(C6F5)(tht)](tht = tetrahydrothiophene), [Au(tht)2]ClO4, and [Ag(OClO3)(PPh3)] to afford binuclear complexes of the types [Au(C6F5){SPh2 PCH[Au(C6F5)]PPh2Me}] or [{M(SPh2PCHPPh2Me)}2][ClO4]2(M = Au or Ag). The silver complex can also be obtained by deprotonation of [{Ag(SPh2PCH2PPh2Me)}2][ClO4]2 with Na2CO3. Oxidative addition of chlorine to the gold derivative gives the binuclear gold(II) complex [{AuCl(SPh2PCHPPh2Me)}2]. The structure of [Au(C6F5){SPh2PCH[Au(C6F5)] PPh2Me}] has been established by X-ray crystallography [space group P21/c, with a= 15.392(4), b= 12.643(5), c= 21.965(7)A, β= 107.95(2)°, and R′= 0.072 for 3 166 unique observed reflections]. The molecule adopts a folded conformation with parallel, eclipsed C6F5 rings and a corresponding short Au ⋯ Au contact of 3.224 A.

A short history of SHELX

Abstract: An account is given of the development of the SHELX system of computer programs from SHELX-76 to the present day. In addition to identifying useful innovations that have come into general use through their implementation in SHELX, a critical analysis is presented of the less-successful features, missed opportunities and desirable improvements for future releases of the software. An attempt is made to understand how a program originally designed for photographic intensity data, punched cards and computers over 10000 times slower than an average modern personal computer has managed to survive for so long. SHELXL is the most widely used program for small-molecule refinement and SHELXS and SHELXD are often employed for structure solution despite the availability of objectively superior programs. SHELXL also finds a niche for the refinement of macromolecules against high-resolution or twinned data; SHELXPRO acts as an interface for macromolecular applications. SHELXC, SHELXD and SHELXE are proving useful for the experimental phasing of macromolecules, especially because they are fast and robust and so are often employed in pipelines for high-throughput phasing. This paper could serve as a general literature citation when one or more of the open-source SHELX programs (and the Bruker AXS version SHELXTL) are employed in the course of a crystal-structure determination.

Crystal structure refinement with SHELXL

Abstract: The improvements in the crystal structure refinement program SHELXL have been closely coupled with the development and increasing importance of the CIF (Crystallographic Information Framework) format for validating and archiving crystal structures. An important simplification is that now only one file in CIF format (for convenience, referred to simply as `a CIF') containing embedded reflection data and SHELXL instructions is needed for a complete structure archive; the program SHREDCIF can be used to extract the .hkl and .ins files required for further refinement with SHELXL. Recent developments in SHELXL facilitate refinement against neutron diffraction data, the treatment of H atoms, the determination of absolute structure, the input of partial structure factors and the refinement of twinned and disordered structures. SHELXL is available free to academics for the Windows, Linux and Mac OS X operating systems, and is particularly suitable for multiple-core processors.

OLEX2: a complete structure solution, refinement and analysis program

Abstract: New software, OLEX2, has been developed for the determination, visualization and analysis of molecular crystal structures. The software has a portable mouse-driven workflow-oriented and fully comprehensive graphical user interface for structure solution, refinement and report generation, as well as novel tools for structure analysis. OLEX2 seamlessly links all aspects of the structure solution, refinement and publication process and presents them in a single workflow-driven package, with the ultimate goal of producing an application which will be useful to both chemists and crystallographers.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

PHENIX: a comprehensive Python-based system for macromolecular structure solution

Abstract: Macromolecular X-ray crystallography is routinely applied to understand biological processes at a molecular level. How­ever, significant time and effort are still required to solve and complete many of these structures because of the need for manual interpretation of complex numerical data using many software packages and the repeated use of interactive three-dimensional graphics. PHENIX has been developed to provide a comprehensive system for macromolecular crystallo­graphic structure solution with an emphasis on the automation of all procedures. This has relied on the development of algorithms that minimize or eliminate subjective input, the development of algorithms that automate procedures that are traditionally performed by hand and, finally, the development of a framework that allows a tight integration between the algorithms.